SERVER-43747 Skip getKeySize for non-unique indexes

1 files changed, 4 insertions, 3 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
index 549475c368e..8cfbac8622e 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
@@ -1162,9 +1162,10 @@ protected:
         // Most keys will have a RecordId appended to the end, with the exception of the _id index
         // and timestamp unsafe unique indexes. The contract of this function is to always return a
         // KeyString with a RecordId, so append one if it does not exists already.
-        auto sizeWithoutRecordId =
-            KeyString::getKeySize(_key.getBuffer(), _key.getSize(), _idx.getOrdering(), _typeBits);
-        if (_key.getSize() == sizeWithoutRecordId) {
+        if (_idx.unique() &&
+            _key.getSize() ==
+                KeyString::getKeySize(
+                    _key.getBuffer(), _key.getSize(), _idx.getOrdering(), _typeBits)) {
             // Create a copy of _key with a RecordId. Because _key is used during cursor restore(),
             // appending the RecordId would cause the cursor to be repositioned incorrectly.
             KeyString::Builder keyWithRecordId(_key);